1. Field of the Invention
The present invention relates to an improvement in the dehumidification of air through the provision of a plate type cross flow air to air heat exchanger having a series of parallel plates enclosed in a housing which conducts flowing air to be redirected for exhaust in a plenum chamber where it is cooled in a two pass flow path through a cooling coil which consists of a plurality of cooling conduits or tubes which are separated by and held as a single unit by a multitude of fins through which cooling conduits pass. The plate type cross flow air to air heat exchanger makes possible a regenerative heat exchange between the intake and exhaust airstreams.
The invention further provides for the cooling coil to be arranged in a manner in which the individual cooling conduits extend in a plane which is parallel to the plane defined by the series of plates, while the fins and the cooling coil unit extend in a plane perpendicular to the plane defined by the series of plates. The cooling coil is positioned in the plenum chamber so that the air flowing through the heat exchanger passes through the cooling conduits twice before it exits the housing. The invention further includes the provision of arranging a number of the air to air plate heat exchangers joined edge corner to edge corner, utilizing a common cooling coil and a common plenum chamber to reduce the cost and size of the system, while at the same time reducing the fan energy requirements for operating the system to condition a large flow of air.
The invention further provides for a manifold assembly with intake, exhaust and baffle dampers and a cooling damper disposed in the condensate collection chamber. The function of the baffle dampers is to make possible an increase in the cooling capacity of the system by providing for cooling of the air stream by passing it through both passes of the air to air heat exchanger simultaneously with the cooling damper open and the exhaust damper closed. The baffle dampers are also open in the bypass and maximum bypass modes, and the lowest possible pressure drop across the system occurs in the maximum bypass mode, in which mode the intake, exhaust, baffle, and cooling dampers are all in the open position.
2. Discussion of Prior Art
Air conditioning in residences, office buildings, commercial structures, and other types of buildings typically requires large amounts of energy to provide comfortable ambient indoor air under a variety of weather conditions, depending upon the climate and the season. Systems that cool and/or dehumidify air are widely employed, whereby as the air is cooled, moisture condenses out of the air resulting in cooler and drier air being returned to the building interior.
In the design of a dehumidifying heat exchanger, an important determination is whether, and how much heating, called in the industry by the term "reheat", will be applied to the air after it has been cooled for the purpose of dehumidifying it. If the cooled, and thus dehumidified air is simply supplied to the ambient interior space without further heating, it is traditional air conditioning, and in doing so, the air may be overcooled in the process. However, in typical dehumidification systems, the air is reheated before being supplied to the ambient interior space. In these systems, one aims to control ambient humidity, not temperature, and the system is controlled by a humidistat which engages and shuts the system down.
In the prior art, there exists a variety of heat exchange devices utilizing a regenerative type of heat exchange airflow in which air passes through the housing in intake channels and is then redirected through exhaust channels. Cooling fluids are provided so that the air passes over the conduits which are typically arranged in a plane perpendicular to the channels and which are in thermal contact with the walls defining the channels, so that the conduits typically pass through the walls. An example of such a regenerative heat exchanger is disclosed in U.S. Pat. No. 2,128,641 to Folsom, which discloses a dehumidifier in which the walls between the channels serve as the heat exchange surface for air as it passes through the intake channels, over the cooling conduits, and then around the channel walls in a plenum chamber into the exhaust channels and back over the cooling conduits. The air is then exhausted back into the atmosphere through exhaust ports located adjacent to the intake ports at the first end of the unit.
U.S. Pat. No. 4,761,966 to Stark teaches cooling and reheating for dehumidification in a cross flow arrangement, as well as an air temperature and water temperature control system for high humidity locations such as indoor pools. U.S. Pat. No. 4,517,810 to Foley et al. teaches regenerative heat exchange using a "run around loop," and Canadian Patent No. 470,100 teaches the use of a corrugated plate in a heat exchange element. U.S. Pat. No. 2,093,725 to Hull teaches the provision of cooling conduits sandwiched between the heat conducting walls of the heat exchanger.
In the prior art heat exchangers, there is generally required a large plenum space to convey the intake air to the cooling conduit or to convey exhaust air leaving the cooling conduit to the final pass through the regenerative heat exchanger. The large plenum space in the prior art could be disposed either upstream of the cooling conduit or downstream of the cooling conduit. Accordingly, prior art heat exchangers required a large area for installation, and also required an excessive amount of energy to force the air through the heat exchanger. Efforts to reduce the plenum space, such as that shown in Folsom, require that the cooling conduits be constructed to pass through the plates of the heat exchanger.
Volumetric efficiency quantifies the required equipment volume in per unit of capacity at a given performance level. In plate type cross flow air to air heat exchangers, to increase the volumetric efficiency and economy of the unit, the smallest possible plate size should be used. However, cross flow heat exchangers with smaller plates require more length, i.e., more plates, to handle air volumes equal to that of units with larger plates. Increasing the plate size will require a larger installation space which may limit the performance of the heat exchanger. In addition, when using cross flow type plate air to air heat exchangers with smaller plates, the length, or number of plates, typically exceeds a required maximum dimension or number and therefore additional rows of small plate heat exchangers are added side by side. The cooling coil, as stated above, consists of a plurality of tubes which are separated by a series of fins serving as a heat transfer surface for the tubes. Generally, cooling coils have many circuits, each circuit comprising a multitude of cooling tubes connected in series, from entrance to exit, using U-shaped bends. Therefore, for economic and efficient cooling coil selection, the cooling tubes in the prior art tend to run substantially perpendicular to the heat exchanger plates. However, this arrangement requires that each cooling tube or tube circuit be separately balanced due to the temperature gradient across the coil surface, because the temperature leaving a cross flow heat exchanger varies in a direction parallel to the plates. As the coolant fluid passes through the tubes, it absorbs heat sufficient to cool the air which passes over the tubes, typically in the range of 35.degree. F. to 55.degree. F. As the heat is absorbed over the length of the tube or circuit, it is most efficient to have substantially equal temperature conditions, and refrigerant superheating, leaving each tube or circuit. In prior art heat exchangers, as seen in FIG. 1, when the tubes are arranged perpendicularly to the plates, the individual tubes or circuits see different temperatures in the air stream, requiring manual, and tedious, balancing of the individual tubes or circuits to ensure equal heat absorption and temperature drops, and thus optimum cooling of the air stream. If the cooling coil of FIG. 1 were placed at the entrance to the exhaust side of the cross flow heat exchanger, performance would improve somewhat because there is more room for mixing of temperature to occur in the plenum chamber. However, the degree of mixing is unpredictable and would be irregular in a confirmed space such as the plenum chamber.
The novel heat exchanger for dehumidification of the present invention obviates the disadvantages associated with the prior art by providing a plate type cross flow heat exchanger having a plurality of plates and a cooling coil consisting of tubes and fins, in which the cooling conduits are arranged in parallel to a plane defined by the plates of the heat exchanger, while the coil fins extend in a plane generally perpendicular to the plane defined by the plates, together with a manifold assembly which includes intake, exhaust, and bypass dampers, and a cooling control damper adjacent to the cooling coil. The cooling coil in the condensate collection chamber is located adjacent to but spaced from the heat exchanger walls while maintaining a seal between the intake channels and exhaust channels as will be described below, and is located in a plenum chamber which redirects the air back over the cooling coil so that a two pass arrangement is achieved as the air passes from the intake channels to the exhaust channels for return to the ambient atmosphere. The heat exchanger of the present invention also facilitates installation in a system which utilizes a number of small units which are operated utilizing a common cooling coil, and may also utilize a common plenum space to reduce the size required for installation and ultimately provide an efficiently operating, energy conserving, and economical system for dehumidifying air in buildings such as residences, office buildings, and commercial structures.